41 - Clinically Relevant Anatomical Variations in the Brachial Plexus

Poster Board Number: 41
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Abstract Body : Anatomical variation in the brachial plexus may result in a variety of clinically relevant symptoms, including various neuralgias of the upper extremity. These conditions can be debilitating in symptomatic patients, resulting in paresthesia, anesthesia, or weakness of the upper extremity. This study evaluated the frequency and anatomical presentations of a large number of clinically relevant brachial plexus nerve variations, paying particular attention to areas in which impingement/compression of the nerve is likely. For this study, a total of 39 (20F/19M) previously dissected human donors from the Anatomy Department at Midwestern University were analyzed from February to July 2022. Analysis involved meticulous cleaning of the brachial plexus, specifically its cords and terminal branches. The nerve branches that compose the “M”, plus the medial brachial cutaneous nerve, medial antebrachial cutaneous nerve, medial pectoral nerve, and thoracodorsal nerve were all traced from their origin to insertion points and branching variations were noted. True prevalence values for each variant were calculated by dividing the number of affected limbs by the number of limbs that could be scored for that variant.

We identified a high frequency of various branching variants of which clinicians should be aware. A classic “M” pattern was observed in only 38% of the sample. The medial pectoral nerves in 30% of the sample were found to originate from either the lateral cord or both the medial and lateral cords of the brachial plexus rather than exclusively from the medial cord. The dual cord innervation pattern greatly increases the number of spinal cord levels traditionally believed to innervate the pectoralis minor muscle. The thoracodorsal nerve arose as a branch of the axillary nerve 17% of the time. The musculocutaneous nerve sent branches to the median nerve in 5% of specimens. The medial antebrachial cutaneous nerve shared a common trunk with the medial brachial cutaneous nerve in 5% of individuals and derived from the ulnar nerve in 3% of specimens. Such nerve variants have specific clinical implications for thoracic outlet syndrome, a relatively common condition affecting up to 8% of the U.S. population. Current diagnostic and treatment modalities are typically based on an underlying assumption of a classic anatomical relationship among the nerves of the brachial plexus; however, this is often not the case. Awareness of these nerve variations may improve patient outcomes, especially surgically. Nerve anomalies may also be visualized using ultrasound if a physician is aware to look for them in advance of a procedure.